This invention relates generally to ultrasonic flow measurement, and more particularly to an ultrasonic waveguide assembly applied in the flow measurement.
Ultrasonic flow meters are used to determine the flow rate of a variety of fluids (e.g., liquids, gases, etc.) and combinations of different fluids flowing through pipes of different sizes and shapes. One type of an ultrasonic flow meter employs a transit time method. This technique uses one or more pairs of ultrasonic transducers attached to the exterior of the pipe wall and located upstream and downstream from each other. Each of the transducers, when energized, transmits an ultrasonic signal through the flowing fluid that is detected by the other ultrasonic transducer of the pair. The velocity of the fluid flowing in the pipe can be calculated as a function of the differential transit time of ultrasonic signals as between (1) the ultrasonic signal traveling upward against the fluid flow direction from the downstream ultrasonic transducer to the upstream ultrasonic transducer, and (2) the ultrasonic signal traveling downward with the fluid flow direction from the upstream ultrasonic transducer to the downstream ultrasonic transducer.
The pair(s) of transducers can be mounted on the pipe at different relative locations, for example, the pairs of transducers can be located on opposite sides of the pipe, i.e. diametrically opposed, such that a straight line connecting the transducers passes through the pipe axis or they can be located adjacently on the same side of the pipe. In the diametric example, the ultrasonic signal transmitted by one of the transducers in the pair of transducers is not reflected off of an interior pipe surface before it is detected by the other transducer in the pair. In the latter example of adjacent transducers, the ultrasonic signal transmitted by one of the transducers in the pair of transducers is reflected by an interior surface of the pipe before it is detected by the other transducer in the pair.
In some applications, the pipes to which the ultrasonic flow meters are attached carry fluids that cause the pipe walls to reach relatively high temperatures, or the pipes may carry fluids that cause the pipe wall to reach relatively low temperatures. Consistent exposure to extreme temperatures introduces thermal stresses that diminish the useful life of the transducer. A waveguide coupled between the ultrasonic transducer and the pipe helps to prevent the extreme temperatures from damaging the piezoelectric material. However, the signal quality can decline due to poor acoustic coupling between the waveguide and the pipe wall caused by, for example, use of manual temporary attachment methods, or by poor acoustic coupling between the launch point of the ultrasonic signals into the fluid traveling through the pipe caused by accumulation of contaminants at the launch point, or by deterioration of the piezoelectric material in the transducer caused by exposure to harsh environments such as temperature extremes.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.